The invention relates to a chamber filter press.
Conventional chamber filter presses consist of a horizontal stack of chamber plates secured to each other, which, in each case, have a recess on both sides and are provided with a filter medium, as for example, a filter cloth. Two filter media, provided between each pair of two adjacent chamber plates, divide the inner space, formed by two adjacent recesses, into a central hollow space for receiving pulp and, on the chamber-plate side, two hollow spaces for receiving filtrate, which are connected with a pulp feed pipeline and a filtrate discharge pipeline respectively. After the filtering operation, the chamber plates are moved apart consecutively in order to remove, in each case, the two filter cakes to be found on the two filter media lying opposite to each other. Before the chambers of these chamber filter presses are opened, the filter cakes can be washed with a suitable liquid, usually water, which is supplied over the pulp feed pipeline. Subsequently, for dewatering, the filter cakes can be treated with compressed air, which also can be supplied over the pulp feed pipeline. In addition, it is possible to act upon the hollow spaces that receive filtrate with a vacuum, for which purpose the filtrate discharge piepline can be connected with a vacuum pipeline or a vacuum source. In order to achieve the lowest possible residual moisture content in this filter cake, it is furthermore known that a flexible membrane may be provided, which is pressed against the filter cakes on the side facing away from the respective filter medium by means of a pressurized liquid medium, usually water under pressure.
All known chamber filter presses have only a limited capacity. The filter cakes must therefore be removed at relatively short intervals and consequently, it takes much effort to operate these presses, particularly since it is relatively difficult to remove the filter cakes with the required degree of thoroughness. The known chamber filter presses furthermore are heavy, especially because of the heavy, material-intensive, supporting structure for the chamber plates, which requires additional space. A continuous, automated method of operating over longer periods of time with little effort on the part of the operator is not possible. Moreover, desired filter cake quality can also not always be achieved. For example, it happens frequently that, when the filter cake is treated with compressed air, it develops cracks, through which the compressed air passes and is ineffective.
The so-called plate and frame filter presses represent a modification of the chamber filter presses. These differ from the actual chamber filter presses only due to the fact that a frame, which encloses the hollow space for receiving the pulp, is inserted between two adjacent chamber plates. The problems mentioned above are also associated with the plate and frame filter presses.
Chamber filter presses are also known, in which the chamber plates are arranged in a vertical stack and two adjacent chamber plates in each case form a chamber consisting of a hollow space for receiving pulp as well as a hollow space for receiving filtrate on the one or the other side of a filter medium. In order to remove the filter cake, the chamber plates are lowered so that the chambers, which are on top of one another, are opened consecutively from the top to the bottom. The filter medium is formed from an endless filter cloth belt, which is passed in zigzag fasion between the chamber plates and, after the chambers are opened, is driven to dispense the filter cakes on two opposite sides of the pulled-apart stack of chamber plates, whereby the filter cloth belt subsequently can be run past spray jets, in order to be washed with a suitable liquid, usually water. These chamber filter presses have the same disadvantages as those described above. However, the most disturbing feature is that the filter cloth belt tears frequently, resulting in frequent down times and expensive repairs.
The art also includes so-called process filter equipment. Besides the actual filtering process, such equipment enables other processing steps to be carried out, such as stirring, heating and/or cooling, evaporating and drying to be carried out in order to treat the medium added. These processing steps can be conducted in a closed space, so that harmful products cannot reach the surrounding atmosphere, although the possibility of this is not excluded while the filter cakes are being removed. This equipment, however, has an extremely low filter capacity, since it is provided with only a single filter medium which covers the cross section of the interior space. Moreover, it is necessary to resort to expensive measures in order to remove the filter cake.
It is an object of the invention to provide a chamber filter press wherein each chamber has a hollow space for receiving pulp and a hollow space for receiving filtrate on one or the other side of a filter medium respectively, and which can be opened after the filtering process for removing the filter medium and from the respective hollow space and for receiving the pulp. The press, while having a simple and light construction and requiring the least possible operating effort, especially as a result of automatically and thoroughly discharging the filter cake from the chambers, has a higher capacity and is able to filter over longer periods of time. Yet it permits the achievement of an exceptionally high filtrate and filter cake quality, including an exceptionally low filter cake moisture content. The press can be so constructed that no substance can escape into the surrounding atmosphere, not even while the filter cakes are being removed from the chambers.